Bob Ross

I'm either trying (so far unsuccessfully) to extend the life of a ~17-year-old DuraAce rear derailleur, or I'm wasting my time...but if anyone has any experience with similar issues and can offer suggestions, I am all ears.

Not sure exactly what series the DuraAce RD is -- it came stock on a 2006 Cannondale Synapse whose drivetrain was otherwise all 6600-series Ultegra. Maybe it's a 7700? And I remember having this issue before, maybe 10 or 12 years ago: the derailleur wouldn't keep consistent tension on the chain, so it and the jockey wheels/cage would occasionally swing forward under tension, causing sloppy shifts and/or dropped chains. I vaguely recall the diagnosis from the LBS mechanic I brought it to back then was "You've got a bad B-spring." (?) ...or something like that?

But he did something -- I know he did a lot of cleaning and lubing, I also know he did not replace that spring...but I don't know what else he may have done at the time -- and so it's worked fairly reliably for these last 10-12 years

...until this week. It's happening again. So, is there anything that can be done besides more thorough cleaning/lubing around the B-pivot area? Can that B-spring be replaced? Should I just be grateful that I was able to get 17 years of good hard use out of it and replace the RD? (Apparently I have a spare 6700-series Ultegra RD on hand that could be used.)

Appreciate your thoughts. Thanks.

smd4

The B spring is definitely replaceable if you can find one—perhaps from a trashed donor RD. For the 7700 (and maybe others—I only have the 7700 schematics), there were two springs available— one for long cage and one for short. I would think one or the other would have a little more power.

Taking the B axle assembly apart isn’t for the faint of heart, but is possible. There are only two anchor holes for the spring, one in the derailleur body and one in the cover, so no option to get more tension by moving the spring to a different hole.

If the spring was broken you would definitely notice so maybe it’s just gummed up.

FBinNY 

Springs are amazingly reliable, so the B-spring itself is the last thing I'd suspect unless it was completely dead.

These RDs depend on a balance between upper and lower springs, so are very sensitive to friction at either pivot.

Best solution would be proper disassembly, cleaning, and tubing.

However being the lazy $#@%&$ I am, I'd start by squirting some solvent at both pivots, wiping dry, and oiling. Followed by a martini while I wait for it to work.

Kontact 

Put something between the screw and the hanger. I've used a little chunk of credit card.

You could also drill a new spring hole.

Kontact 

Say what? Shimano B springs always get soft over time. Seems like every DA and Ultegra bike I've worked on that was a few years old had the B spring buried just to clear a 27t cog.

smd4

And yet people here always claim that springs don’t lose their tension.

Kontact 

Because they were told an oversimplified version of reality and keep repeating it like its true.

The truth is that springs are operating a cannibalistic child molesting ring out of pizza parlor in DC.

Dave Mayer

Dura-Ace 7700 and 7800 is outstanding kit, and it should be restored if at all possible. Some lesser derailleurs are not worth the trouble, but this gear is.

First off, derailleurs should not be cleaned with water or anything water based. I've seen high-end derailleurs and hubs seized up solid with corrosion due to the owner's over-ambitious and misguided efforts at 'cleaning' them. If they are really dirty and are getting 'stiff', then they should be disassembled right down to the parallelogram, and then cleaned and regreased. The 4 parallelogram pivots should be lubed with a light oil. The A and B springs should be removed and relubed. Of course the jockey wheels should be taken apart to the bushings and relubed with grease.

I have never taken apart a derailleur whose springs were not restored to full 100% 'springiness' when serviced adequately.

This is complex and picky work, particularly the first time, but worth it for this class of gear.

smd4

To be pedantic, what you refer to as the A spring, Shimano refers to as the “P-Tension Spring.” “P” standing for “pulley,” it’s assumed.

Kontact 

Do you recommend only cycling in tunnels on rainy days, or do you wrap a plastic bag around the derailleurs to prevent the corrosion that aluminum apparently gets from fresh water?

smd4

I was going to write something smart-ass-y too about cleaning a derailleur in water but thought better of it.

Dave Mayer

To the OP: ignore most of the previous useless contributions to this thread - zero value. Just bores who overvalue their own inexperience.

BTW: Engineering 101 is that metal springs do not change unless they are stretched beyond the yield point. I have disassembled dozens of high quality derailleurs and restored almost all of them to full function. Never seen a spring get 'soft'.

In contrast, here is something useful:


The difficult part starts at the 9:00 minute mark.

Kontact 

Where's the yield point in a Shimano B spring?

smd4

In the DC pizza parlor basement. Duh.

Dave Mayer

Again, thanks for this useful contribution to this thread and the task faced by the OP. Another irrelevant and useless waste of thread bandwidth.

The only time derailleur springs get distorted beyond the yield point is when the derailleur has been in a crash or ended up in the spokes, which is easy to determine. I've pulled hundreds off bikes, most irrecoverable.

Again, please enlighten us with your deep experience in recovering rear derailleurs as in the video, and operation that I've done successfully dozens of time.

Kontact 

Well Dave, you said the springs stick or something due to water corrosion, and that you shouldn't clean it with water. Then you posted a video of overhauling a derailleur which has no corrosion and is cleaned with soapy water. Which is why some of your posts seem amusing.

So is the problem with the springs corrosion? Are they just lacking lubrication? Would the spray lubricants I've tried in the past completely fail to restore function because the B mechanism is so incredibly well sealed, or because the corrosion is so incredibly implacable? It isn't like the ones I've dealt with have a range of motion problem or noticeable friction - they just don't spring in their original range, and that range has migrated counterclockwise.

And your reply about yield point doesn't make a lot of sense, except as a statement of faith that Shimano didn't design a derailleur whose range of motion is beyond the spring's limits. I've dealt with tons of devices that wear their springs out because of the way the device works and the somewhat inadequate spring specification.

rccardr 

Thanks for the video. That trick with the allen key to tension the spring and install the backing plate before inserting the C clip is pretty slick.
Learned something new!

Dave Mayer

Right, yes the use of a small hex key to rotate the backing plate before pressing it against the spring is the single most important tip in all of this. This step would drive me crazy until I figured this out pre-Youtube. Sometimes you need a small set of vice grips to (carefully!!) compress the backing plate against the spring tension. Since the Dura-Ace and XTR units have alu backing plates, extra caution is required, as this plate is easily bent, unlike the steel plates found in the lesser derailleurs.

On the subject of water: don't use a pressure washer to clean your bike. The derailleurs that I've been handed seized up and misdiagnosed as "having bad springs" all had this problem. Upon disassembly, not a trace of grease/lube left in the 2 cavities, but just corrosion. Water has no place in bike maintenance; if you need a degreaser, then there more effective and less corrosive products, such as mineral spirits.

70sSanO

I'm in the nothing is absolute camp. Everything has a life cycle and every manufacturing company subs out the manufacture of different individual parts and sub-assemblies. Something as simple as an internal cam skewer has been the subject of a Shimano recall 20 years ago, not the Trek one. And the recent Shimano crank recall will be legendary.

The first step is to follow the video and disassemble the RD. It is not that tough and doesn't require any special tools. Unless you have never maintained your RD and it looks like the one in the video, the cleaning may or may not solve it. Those who have gone through the process and returned a RD to full max cog capacity have more experience than I have.

That said, I have found a couple of RD's that "seem" to have weak B springs. I'm using an M910 on my road bike. I bought it used. The anodizing had faded and the jockey wheels were cracked. But it wasn't beat up. Replaced the jockey wheels and mounted it and have been using it for almost 10 years; the last couple running a 36t cog. The RD is rated for 32t. I ran an M950 on my wife's road bike. Over time it would not clear a 32t. Can't say if the springs were going or needed cleaning, but it was in much better condition than my M910.

I have had a similar issue with a couple M580 Rapid Rise that were bought new. Ridden in dry, paved conditions with few miles and both eventually had trouble clearing a 32t and 34t respectfully. My current solution was to fashion a block from a nut and added it to the end of the B screw to add more tension and still connect to the hanger tab. I'm running an M760 on my mtb in crappy conditions, dust, dirt, mud, dumped in a stream or two and have not had an issue with running a 34t. I have recently added a RoadLink and I'm running a 40t, so it is now not apples to apples. But both are the same era and the M760 has not demonstrated the same cog clearing issues. I will one day disassemble the M580 and see if it returns to normal. If it does, or doesn't, I pass it along down the road.

John

Kontact 

Why do you talk about seized derailleur B pivots when I thought we were talking about decreased spring authority with normal movement?

masi61

When corrosion gets into the tight cylindrical sleeve between the pivot bolt the (B?) pivot spring becomes lethargic and lazy about wrapping chain. My Ultegra 6500 GS long cage RD’s pivovot bolt did this last year which was manifesting as near ride ending mystery chain crunching quick disengagement when trying to stand to climb in my 30 tooth granny front chainring. The bolt was so corroded in that near interference fit sleeve that even when sprayed with liberal amounts of PB Blaster, I still needed to tap the bolt out with a punch and a hammer. And as Dave here has stated, there will be absolutely nothing wrong with the spring. So I had refreshed the pivots on that 6500 GS RD last year with healthy amounts of Rock-N-Roll Super Web Grease and I thought the derailleur would be snappy and responsive again but somehow the lethargic chain wrapping issue has recurred after just ~1 year of average road riding with an average amount of rain rides where you get caught out in a storm and have to return home in a heavy downpour (multiples of x’s). So it will be another exploratory disassembly of the 6500 GS RD to see what the malfunction is…

Dave Mayer

Exactly. I have seen many rear derailleurs where one or both pivots are so corroded that they barely move. Or the 4 pivots in the parallelogram cage are similarly corroded and need some lube to be worked into them. Again, I have successfully recovered dozens of quality rear derailleurs to full (as new) function through disassembly and servicing. To reply to Kontacts unintelligible and time wasting postings here, the only derailleurs in which the springs were any way compromised were as a result of severe damage, as in getting stuck in the spokes, or a squirrel.

Bill Kapaun

I think it took 3 days for them to make my Ignore List for the same reasons. People who believe in quantity of posts vs QUALITY of posts.

Kontact 

So what about the ones that move easily, but the B screw doesn't make them go into the right position?

KerryIrons

Agree completely with this!